Warp Zones and .ini files

In this tutorial about Warp Zones: http://udn.epicgames.com/Content/ExampleMapsWarpZones
there's the following:
"Before you start on creating your WarpZones, you will want to make sure that you follow these guidelines

bUseStencil = True Make sure you have this set option in your .ini file set to true. You will need to exit Unreal Ed, go into your system folder open up your yourgam.ini/ file (in a clean build from UDN, that would be the _UW.ini file), search for “UseStencil” and set that value to True. If you don’t know which .ini file to update, ask a programmer."

Now, I have no "_UW.ini" like file in my system folder. I just got these:

Default.ini
DefUnrealEd.ini
DefUser.ini
Manifest.ini
UDNHelpTopics.ini
UE2Runtime.ini
unrealed.ini
UnrealEdTips.ini
User.ini

Which one is the right file to edit?

Thanks

Ok I found a solution: View>Advanced Options>Rendering>Direct3D Support>UseStencil=True. It seems to work in displaying correctly the map

Cheers!